1. Technical Field
The present invention relates to a liquid discharge apparatus, a head unit, and a control method of the liquid discharge apparatus.
2. Related Art
As an ink jet printer that discharges ink and prints an image or a document, a printer that uses piezoelectric elements (for example, piezo element) is known. The piezoelectric elements are provided respectively corresponding to a plurality of nozzles in a head unit (print head) and are respectively driven in accordance with drive signals and thereby a predetermined amount of ink (liquid) is discharged from the nozzles at a predetermined timing. The piezoelectric element is a capacitive load like a capacitor in terms of electric power and a sufficient current is needed to operate the piezoelectric element of the nozzle.
Therefore, in the related art, a configuration is known, in which the drive signal is amplified by using an amplifier circuit and the amplified drive signal is supplied to the head unit such that the piezoelectric element is driven.
In a case where gradation is expressed in such a configuration, a configuration is also known in which two types or more of drive signals are prepared and the amplified two types or more of drive signals are combined according to the gradation and supplied to the piezoelectric element. For example, when A waveform and B waveform, each of which has a first half pattern and a second half pattern as a drive signal are prepared, four types of (A-A), (A-B), (B-A), and (B-B) are formed as the combinations (first half-second half). When a combination is selected in accordance with the gradation from the four types and supplied to the piezoelectric element, an amount of ink in accordance with the gradation is discharged such that it is possible to express the gradation.
As a switch that selects a combination in accordance with the gradation from A waveform and B waveform, a transfer gate is often used. The transfer gate is not formed to have a simple configuration in which a P type and an N type are combined. This is because a voltage range of the amplified drive signal, that is, a drive voltage range of the piezoelectric element, reaches a range of 0 volts to 42 volts. Therefore, a transfer gate is proposed, in which a so-called floating gate is employed and, while a small potential difference between a gate and a source with respect to a change of an input/output voltage is maintained, switching is performed (see JP-A-2004-363997).
However, the transfer gate described above has a complex configuration and power consumption thereof is great. When the configuration of selecting from A waveform and B waveform is provided, two sets of transfer gates are sufficient as a switch, but in a case where a pseudo-resolution becomes high or the like, three sets or more of transfer gates are needed, and thus a complex configuration and high power consumption are problems to be solved.